1. Field of the Invention
This invention relates generally to the field of automotive diagnostics, especially internal combustion engine diagnostics, and more particularly to the problem of automatic, real time engine waveform feature extraction for exact trouble pinpointing.
2. Description of the Related Art
Engine analyzer systems typically consist of signal pickup probes, a processor, and an oscilloscope display that can be synchronized to the engine RPM. In particular, waveform analyzers may contain capacitive or magnetic pickups on spark plug wires and direct or probe connections to primary conductors, as well as probes to sources of fuel injector signals, alternator signals, oxygen sensors, and other possible sensors. These probes respond to the electrical signals that control the functioning of the engine. The electrical output signals from the probes are usually amplified and conditioned for display on an oscilloscope screen. Modem analyzers may also sample and convert the signals to digital form before display. A processor may manipulate the signals so that the digital display shows a reconstructed simulation rather than the actual analog waveform that occurred during a cylinder firing cycle.
The purpose of analyzing engine signals is to diagnose malfunctions and aid in tuneup and adjustment of engine control systems and devices. Engine signals, when properly interpreted and analyzed, can point to a myriad of possible problems. Analysis generally proceeds in one of two ways. The waveforms are either displayed on an oscilloscope where a trained human operator interprets their condition and searches visually for anomalies, or they are stored in a memory and later processed off line (not in real time). In either case, post processing and interpreting waveforms and examining features is very slow. For the case of an oscilloscope display, the waveform is overwritten numerous times while the operator examines it. It is possible to miss transient problems because an operator is really observing the average of many engine or cylinder cycles. For the case of off-line processing, a series of engine cycles is stored. Some are analyzed, while others are ignored. Transient conditions present in unstored or ignored waveforms are missed.
There is a need for a method and apparatus to extract and analyze features from engine signals in real time. Such a system must be able to examine every engine cycle and every cylinder period completely before another occurs. A plurality of waveform parameters must be extracted and analyzed for anomalies, both against fixed thresholds and against running averages. Important features should be stored, and anomalies must be reported in real time. In addition, real time waveforms should be marked indicating that an abnormality has been detected and what that abnormality was. The waveform can be later reconstructed and displayed with the anomaly clearly marked. The system should be able to analyze both primary and secondary ignition waveforms as well as other engine waveforms. In particular, the analysis of ignition waveforms should include different characteristic parts of the ignition waveform such as firing peak, firing line, oscillations, and dwell. The system must not miss targeted transient conditions.